1. Field of the Invention
The present invention relates to a liquid crystal display device for displaying various kinds of information, and more particularly to a liquid crystal display device which has a liquid crystal display with a memory effect.
2. Description of Related Art
Recently, displays which use liquid crystal are widely used. There are various kinds of liquid crystal displays, and as a type of display with a memory effect, a reflective type liquid crystal display which uses ferrodielectric liquid crystal or cholesteric liquid crystal is known. A well-known TN type liquid crystal display repeats writing at intervals of a very short time so as to keep displaying an image thereon, that is, executes a refresh drive. A liquid crystal display with a memory effect, on the other hand, an image written thereon is kept even after stoppage of application of a driving voltage, which is good in energy saving.
However, such a liquid crystal display with a memory effect has a problem that when someone touches the screen while the display keeps an image thereon, the image may be disordered and the disordered image may be kept thereon.
By way of analogy, since a refrigerator has a flat and plain surface, generally, memos and recipes are stuck thereon by magnets or an adhesive tape, or a white board is magnetically fitted onto the surface so that schedules or other information can be written thereon by a marker. In such ways, however, the volume of information to be displayed is limited, and in the case of using a white board, when the written information is erased, rubbish may be dispersed, and the writer may smudge a hand. Also, in these cases, what are written and displayed are only letters and schemes, and it is difficult to write accurate images.
Japanese Patent Laid Open Publication Nos. 9-19768 and 8-35759 disclosed that a liquid crystal display is provided on the surface of a refrigerator. The displays suggested by these documents are of a type which uses liquid crystal without a memory effect and consumes electric power to keep displaying an image thereon. Refrigerators consume great electric power compared with other household electrical appliances, and to reduce the consumption of electric power of refrigerators is a big task in view of energy saving. Providing a liquid crystal display without a memory effect to a refrigerator results in an increase in the consumption of electric power of the refrigerator, which is against the demand of the times. Even if such a liquid crystal display without a memory effect is used, by using a timer to shut off supply of electric power to the display after a specified time, energy saving can be achieved. In this case, however, the image on the display will be erased simultaneously with the shut-off of supply of electric power.